Time Traveling 'Aliens'?

So I have been asking myself various questions since coming to these forums, mainly, Why would those that KNOW about Aliens/UFOs/Grays/Whatever hide them from those of us that DONT know about them? Then I started to think about something my grandfather told me once when we were talking about the subject.

His personal belief is that the 'UFOs/Aliens' we see are evolved from human and that they are coming back in time as historians, or maybe because they are having trouble with a microbial issue and do not have the means to fight it naturally.

He thinks that out future selves are only able to travel backwards through time for some reason and eventually travel far enough back in time to a point before humans civilized certain parts of the world and created a wonderfull community we now call Atlantis.

Is there any proof of any of this? Not that I have ever seen, though admittedly, I never really looked. However, if someone was travelling backward through time, and we didn't want to interupt OUR future, it would make sense to keep information gained from these beings secret as to not upset the balance of our timestream.

Anyone have any thoughts?

i'm sure we'll eventually be able to time travel... if it can be imagined, it can be possible at some point... i wouldn't doubt if peeps from the future come back to look in on us from time to time, perhaps for research, to take a vacation or perhaps just to laugh at us, who knows... but it's an interesting concept nonetheless...